1. Field of the Invention
The present invention relates to a process for preparing carbonyl compounds, more particularly, to a process for efficiently and consistently preparing carbonyl compounds, which include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, etc. and aldehydes such as acetaldehyde, etc. by oxidizing olefins.
2. Description of the Prior Art
Organic carbonyl compounds, which include ketones such as acetone, methyl ethyl ketone, methyl isopropyl ketone, cyclopentanone, etc., are useful as solvents and primary chemicals, etc.
As a process for preparation of carbonyl compounds by direct oxidation of olefins, there is known the so-called Wacker process, in which a PdCl.sub.2 -CuCl.sub.2 system is employed as a catalyst. The Wacker process has some defect such that the reaction rate remarkably decreases as the number of carbon atoms of the starting olefin materials increases, and the reactivity of the internal olefins is poor. Further, the Wacker process requires a relatively large quantity of active chlorinated compound so that it causes problems of corrosion of equipment, formation of by-product chlorinated compounds, and so on. Therefore, the Wacker process is industrially applicable only to the production of lower carbonyl compounds such as acetaldehyde and acetone.
Under the circumstances, recently several novel processes have been proposed, in which improvements by modification of the catalyst system and the solvent system are attempted.
Japanese Laid-Open Patent Publication (Kohyo) No. 63-500,923 proposes a process using a catalyst system in which a redox metal such as Cu, Fe, Mn or the like and/or a ligand such as acetonitrile or the like are added to a Pd-polyoxoanion system.
In this process, the addition of only one of the redox metal or the ligand does not remarkably improve the catalyst activity, that is, the improvement of the catalyst activity depends largely on the synergistic effect of the redox metal and the ligand. Hence, the process involves a problem that the catalyst system is complicated, and therefore, separation and recovery of the catalyst components are difficult as in conventional processes described hereinabove. Further, this process presents a serious problem that the catalyst components precipitate as the reaction proceeds, and thereby the reaction rate drops to a remarkable low level, although the reactivity in the initial stage of the reaction is relatively good.
Japanese Examined Patent Publication (Kokoku) no. 49-024451 discloses a process in which olefins are oxidized with oxygen using a Pd-phosphine complex or a Pt-phosphine complex.
In this process, the activity of the active catalyst species Pd.sup.2+ is poor and regeneration thereof is insufficient, although the reaction catalytically proceeds. Also, the catalyst components precipitate at the early stage of the reaction and are deactivated.
French Patent Specification No. 2,638,739 discloses a process in which a Pd-AgNO.sub.3 -(phosphorus compound) system is used as a catalyst.
In this process, the catalyst activity is not so good and it is a problem that expensive AgNO.sub.3 must be used as an oxidizing agent.
Japanese Laid-Open Patent Publication (Kokai) No, 55-92333 discloses a process in which a Pd-(phosphorus compound) complex and peroxide compound is used as a catalyst.
In this process, it is a problem that catalyst activity is poor and the oxidizing agent used such as a peroxide is expensive.
Further, U.S. Pat. No. 4,532,362 discloses a process, in which a Pd-(heteropolyacid or Cu)-(phase-transfer catalyst)-(perfluorodecaline) system is used with a hydrocarbon/water as a solvent.
This process has a defect that the catalyst activity is poor. In the specification, Pd-phosphine complex is referred to but nothing is described concerning the effect thereof.
Further, Japanese Laid-Open Patent Publication (Kokai) No. 3-106844, a process for preparing carbonyl compounds characterized by oxidizing chain olefins in the presence of a Pd compound and a polyoxoanion compound in a solvent comprising alcohols. This process is satisfactory in that the initial activity of the catalyst is excellent and the high catalyst activity is well maintained over a long period of reaction of no less than 2 hours as described in the working examples in the specification.
In this technical field, however, recently a demand has arisen for a catalyst which can maintain catalyst activity for the reaction time far longer than that described in the above described patent.
The above-described process using the catalyst system comprising a Pd-compound and a polyoxoanion compound is superior to the Wacker process in which a large quantity of active chlorine compounds (CuCl.sub.2, HCl, etc.) in that problems of corrosion of the apparatuses and formation of chlorinated by-products is reduced and there is an expectation of further improvement in catalyst activity and olefin reactivity. However, the process is not free from the above described various problems and thus cannot yet commercially employable. Therefore, development of a new process which solves the above described problems and practically applicable has been strongly desired.
We made an intensive study to solve the above problems and we found that deterioration of the catalyst activity caused by precipitating of Pd can be prevented and the catalyst performance and high reaction rate can be stably maintained by conducting the reaction in the co-presence of an organic phosphorus compound when carbonyl compounds are prepared by oxidation of olefins using a catalyst system comprising a palladium compound and a polyoxoanion compound such as heteropolyacid.
It was found that this process is remarkably advantageous since the process does not require use of a large quantity of the polyoxoanion compound, is free from apparatus corrosion, and separation of the product from the reaction system, and recovery and recycling of the solvent and the catalyst or the components thereof are easy.
Therefore, the object of the present invention is to solve the above-described problems and provide a process for preparing carbonyl compounds (aldehydes, ketones, etc.) by oxidation of olefins using a catalyst system comprising a palladium compound and/or a palladium metal and a polyoxoanion compound such as a heteropoly- or isopolyacid, etc., wherein deterioration of the catalyst activity of the Pd catalyst caused by precipitating of the catalyst component in the form of palladium black is prevented, the catalyst activity is well maintained and thus the object carbonyl compound is prepared with high efficiency and high productivity.